A gyrocopter is an aircraft that flies using a combination of a powered propeller and an unpowered set of rotary wings. The propeller provides the aircraft with forward thrust, and the rotary wings (or rotor) autorotate to generate a lift as a result of the forward thrust of the aircraft. Unlike a helicopter, a gyrocopter typically requires some length of runaway for both take-off and landing. Unlike a fixed wing aircraft, the ability of the rotor to autorotate as the gyrocopter gains forward speed significantly reduces the distance required for both take-off and landing.
One approach used to further reduce the gyrocopter's take-off and landing distance is to pre-rotate the rotor so that it begins generating lift before the gyrocopter begins to move in a forward direction. In a typical arrangement, a gyrocopter pre-rotator uses power from the gyrocopter engine (which otherwise produces power for the thrust propeller), for example, via a clutched drive drum or drive wheel combination. The drive system typically includes a drive shaft having a first gear that engages with a corresponding second gear carried by the rotor. The drive system can include a flexible shaft or a fixed shaft, such as a shaft coupled between universal joints.
One drawback with the foregoing approach is that the gyrocopter rotor typically has a fixed pitch. As a result, the lift generated by the rotor (when powered by the pre-rotator) is typically not enough to eliminate the need for a runway. Accordingly, one approach to address the foregoing problem is to provide the rotor with a collective pitch control. In operation, the pitch control is initially set to zero pitch to reduce the drag on the rotor and reduce the requirements for spinning the rotor up. Once the rotor has been spun up, the pitch of the rotor blades is suddenly increased, causing the gyrocopter to rise suddenly in a “jump take-off” maneuver.
However, the “jump take-off” system also has drawbacks. For example, this approach can significantly increase the complexity of the rotor head because the rotor head must be configured to pitch the rotor blades. As a result, the initial cost of the gyrocopter and the level of maintenance required to keep the gyrocopter in operation may increase to the point where the gyrocopter is nearly as costly as a helicopter. In such instances, many commercial operators prefer a helicopter, which does not need a pre-rotator for zero distance take-offs. Accordingly, there remains a need for cost-effective gyrocopters that require no take-off or landing roll.